I saw the terms. Charities are excluded. From their website:
The following types of merchants are not eligible: those that are part of a franchise brand with more than 100 stores (if a franchise brand has more than 20 corporate-owned stores, then the entire brand is excluded) and merchants who accept American Express Cards solely through a third party payments aggregator, including those that offer the ability to accept credit cards through a card reader attached to a mobile device, or as part of an affiliate program.
Merchants in the following categories are also not eligible: government agencies, public administration, charities, non-profits, trade associations, shopping property management companies, direct sellers, and political organizations.
Merchants that do not have a physical storefront or location are not eligible and will not appear on the Small Business Saturday Map which will be available from 11/21/13-12/1/13.